The long term goal of this project is to translate novel findings in the field of innate immunity into early phase immunotherapy clinical trials for patients with hematologic malignancies. In this proposal we focus on acute myeloid leukemia (AML), an aggressive cancer of developing myeloid cells that has a poor prognosis, with <30% of patients treated with standard therapy achieving long-term disease-free survival. While allogeneic hematopoietic cell transplantation (HCT) is a standard treatment that is potentially curative for some patients with AML, this therapy is associated with significant morbidity (graft versus host disease and infection) and treatment-related mortality. This limits HCT applicability and overall effectiveness in this disease of older individuals. One promising strategy that preserves the anti-leukemia effector function against AML, without the morbidity and mortality of HCT, is the adoptive transfer of allogeneic lymphocytes. Natural killer (NK) cells are innate lymphoid cells that are specialized to eliminate malignantly transformed target cells. Clinical studies for AML patients using HLA-haploidentical allogeneic HCT have shown that the reactivity of donor NK cells against the patients' leukemia predicts for long-term disease-free survival. Adoptive immunotherapy with enriched allogeneic NK cell products administered to patients with active AML have resulted in complete remissions, although these are achieved in a minority of patients and are of limited duration. We hypothesize that enhancing NK cell recognition of, and effector function against, AML blasts will result in improved clinical outcomes following adoptive NK cell therapy. Recently, paradigm shifting studies have shown that NK cells exhibit immune memory, a property previously attributed only to adaptive T and B lymphocytes. We have established that human NK cells exhibit innate memory following a brief combined stimulation with interleukins (IL)-12, -15, and -18. Preliminary data demonstrates that memory-like NK cells exhibit significantly enhanced AML recognition, functionality, longevity, and proliferative potential compared to naive or control NK cells. Recent preliminary data also shows that administration of allogeneic memory-like NK cells is safe, feasible, and results in clinical responses in AML patients. Thus, we hypothesize that allogeneic memory-like NK cells administered as adoptive immunotherapy for patients with AML will exhibit potent anti-leukemia responses. In this proposal, we will 1) test the safety and efficacy of allogeneic memory-like NK cell adoptive immunotherapy in a first-in-human phase 1/2 clinical trial for patients with relapsed AML, 2) define memory-like NK cell correlates of clinical response, and elucidate key mechanisms important for memory-like NK cell anti-AML responses, and 3) define the importance of NKG2A as a memory-like NK cell checkpoint, and elucidate mechanisms of AML resistance to memory-like NK cell therapy.